Cache Memory And Cache Battery; Cache Memory - IBM DS3500 Installation, User's, And Maintenance Manual

10. Diagnose and correct the fault.
11. Replace the bezel on the storage enclosure, if applicable.

Cache memory and cache battery

Each storage controller in the DS3500 storage subsystem contains 1 GB or 2 GB of
cache memory to store read and write operations. In a dual controller
configuration, both controllers in the DS3500 must have the same amount of cache
memory. The battery unit contains enough charge to back up the cached data in
each controller to a flash drive in the event of a DS3500 power failure.

Cache memory

Cache memory is memory on the storage controller that is used for intermediate
storage of read and write data on the DS3500 controllers. Using cache memory can
increase system performance. The data for a read operation from the host might be
in the cache memory from a previous operation (thus eliminating the need to
access the drive itself), and a write operation is completed when it is written to the
cache, rather than to the drives.
The controller has a cache active LED that indicates the current status of the cache.
The LED is lit when there is data in the cache, and it is off when there is no data
in the cache.
Note: If there are enclosures with dc power supplies in your storage
subsystem, ensure that the -48V disconnect devices are turned on and are
working.
7. Turn on both power switches on the rear of the storage subsystem. See
Figure 75 on page 84
A storage subsystem can take 10 seconds to power-on and up to 15 minutes
for the battery self-test to be completed. During this time, the LEDs on the
front and the rear of the DS3500 flash intermittently.
8. Check the LEDs on the front and rear of the storage subsystem and each
attached storage enclosure (a green LED indicates a normal status; an amber
LED indicates a hardware fault); then, check the subsystem status in the
Subsystem Management window.
a. Open the Subsystem Management window for the storage subsystem.
b. Click the Summary tab and review the status of the configuration.
The status is either Optimal or Needs Attention.
9. Does each module (controller, power supply, ESM) display green status LEDs
only, and is the status Optimal for each module component?
v Yes: Go to step 11.
v No: Go to step 10.
a. To run the Recovery Guru, click Recovery Guru in the toolbar in the
Subsystem Management window.
b. Complete the recovery procedure.
If the Recovery Guru directs you to replace a failed component, locate and
troubleshoot that component. See "Checking the LEDs" on page 88.
c. When the procedure is completed, select Recheck in the Recovery Guru.
This runs the Recovery Guru again to ensure that the problem is corrected.
d. If the problem remains, contact your IBM technical-support representative.
Chapter 4. Operating the storage subsystem and storage enclosure
101